Method of making joints in wound cores



Nov. 3, 1953 c. w. MOODY METHOD OF MAKING JOINTS IN WOUND CORES Filed Dec. 14, 1948 Inv eTW COT: Charles W. Moqdy, by

H is Attof w ey.

Patented Nov. 3, 1953 UNITED STATES PATENT OFFICE METHOD OF MAKING JOINTS IN WOUND CORES New York Application December 14, 1948, Serial No. 65,193

Claims. 1

This invention relates to wound magnetic cores for electric induction apparatus and more particularly to a new method of making a joint in such cores.

Since the development of magnetic strip material, such as high reduction cold rolled silicon steel, which has highly favorable magnetic properties in the direction of rolling i. e., in the lengthwise direction of the strip, wound cores have increased in importance because they inherently make good utilization of those properties by permitting the magnetic flux to travel always in the favorable direction especially at the corners. However, there has always been a problem in linking such a core with a conductive winding so as to form an operative induction apparatus.

One approach to the solution of this problem has been to wind the conductive winding on the core. This has the advantage that no joints are necessary in the core and that the core need not be disturbed after it has been annealed. The latter is important, because directional steels are very sensitive to mechanical strain and lose a substantial amount of their favorable magnetic properties if the material has been strained. However, this approach has the disadvantage that it is difiicult to get good space factor in the winding window, that is to say, it is difficult to fill the winding window with magnetic materal so that as a consequence the completed apparatus has to be larger than necessary, and it is necessary to use more copper in the winding. Furthermore, leakage reactance is also increased. These disadvantages stem from the fact that the smallest possible cross section of the spool for a conductive winding which is to be wound on a core is circular, which means that if the space factor in such a circular window is to be good the cross section of the core winding leg should also be circular, and it is impractical to obtain such a core leg cross section at low cost. An additional disadvantage of this method is that the means for turning the spool occupies some of the length of the core winding leg and thus space in the inductive device is wasted and it is larger than is electromagnetically necessary.

Another approach to the above problem is to, in effect, wind the core on the conductive winding. While this also has the advantage of eliminating core joints, it has the disadvantages of somewhat straining the magnetic material as it is threaded into the coil Window and of also being limited to round wound cores. Any strains produced when the core is wound through the coil window cannot be removed by annealing, as the high temperatures involved in such an annealing operation would melt the copper in the conductive winding and would also destroy most forms of electrical insulation. The reason that this technique is limited to round cores is that a core which has been tightly wound and annealed and is then in effect unwound and rewound through the coil window cannot be satisfactorily reformed during the rewinding operation if it has any fairly sharp corners, because the turns simply will not fit together again as they did after the original winding operation.

A third approach to the above problem is to provide the core laminations with a joint or joints. While such joints do tend to increase the core reluctance that may it possible to use rectangular cores having straight winding legs with rectangular cross section so that form wound conductive windings having a rectangular window can be used. Heretofore these joints have been formed by cutting completely through all of the core laminations either at one place or zone in the core or at relatively widely spaced places. For example, a wound core can be completely cut through at one or more places so as to form one or more butt joints Alternatively, the individual laminations can be out slightly offset from each other so as to form a lapped joint. Still another way is to unwind a one-piece wound core and cut it into, say, two turn lengths which are individually laced through the coil window so as to build up the core with radially nested two turn lengths all occupying the same relative positions that they had in the original one piece wound core. All of these latter operations require considerable assembly labor, and they all require relatively expensive treatment of the core after it has been originally wound to the desired shape and size.

In accordance with this invention a joint, at least in embryonic form, is wound directly into the core at the time that the core is originally Wound. This is accomplished by repeatedly weakening, as by partially cutting through, the magnetic strip as it is wound on a mandrel to form a core of any desired shape and size with the weakened places occurring at least once in each layer and all lying within a transverse zone through the core which is relatively narrow or short in comparison with the length of the magnetic circuit of the core. In this manner the above-mentioned zone is itself relatively weak mechanically in comparison with the rest of the new and improved method of forming a joint in a wound magnetic core.

The invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing Fig. l is a perspective view of an electric induction apparatus embodying a core made in accordance with the invention which core is normally provided with a winding which indicated in phantom, Fig. 2 illustrates a step in the method of making the core, Fig. 3 is a perspective view from a difierent angle of the fully wound core and illustrating one way of breaking openthe jointinthe'core, Fig. 4 is a Viewsirnilar to Fig. 3 showing how the core joint has been broken open, Fig. 5 shows how the core is flexed after opening the joint for the purpose of linking it with a conductive winding, Fig.

6 is a detailed view showing one way of partially:

cutting through the strip of magnetic material so, as to form the weakened places in the core, Fig. 1

7 is a side elevation of Fig 6 showing a modified formof cut in the strip, Figs 8 and 9 illustrate another method of breaking the weakened places in the wound core so asto complete the joint.

Referring now to the' drawing and more partieularly to Fig 1, there is shown, by way of example, agenerally rectangular shaped woundcore I consisting of a pluralityof radially nested layers of magnetic strip naterial. This core has a generally straight winding leg 2, and the core also. has a'lapped joint 3 which is within the lateralconfines of the winding leg 2. As shown phantom a conductive winding or windings 4 is ordinarily mounted on the winding leg.

As shown in Fig 2, the core is formed by winding a strip of magnetic material 5 on an arbor or mandrel 6 which is mounted for rotation on a shaft 1. For reasons which will, be explained hereinafter the arbor is preferably made in two separable parts Band 9, the former being generally U-shapedand the latter being a flat member which extends between the ends of the legs oftheU-shaped member 8 so as to provide the rectangular form for. the, core. Thestrip 5 is also provided w ith weakened places in any suitable mannersuch as by means of a movable shear member In which cooperates with an edge of a fixed member II which is beneath the strip 5. The lower end or cutting edge of the shear may be provided with a notch or recess l2 so that as theshea r I0 is moved downwardly by any suitable means, such as by hand, strip will be sheared entirely through except for a short portion in the center corresponding to the length of the notch l2. The weakened place formed in this manner is shown enlarged in Fig. 6;

The spacing between successive weakened places. in the strip is such that as the strip is wound onuto the mandrel the weakenedplaces will allfall within a relatively short zone in the core. Due to the fact that the length of the strip forming each successive turn increases as the thickness of thecore increases, the spacing between successive weakened places will, in general, progressively increase. However, with a lapped joint as shown in Fig. 4, the weakened places do not all lie in the same plane through the core but they alternately lie in different planes indicated at 13 and I4. Thus for example, all the weakened places in the odd-numbered layers of the core starting with .the, innermostlayer will lie in the plane l4, and all the weakened places in the even-numbered layers will lie in the plane [3, After the core has been wound to the desired thickness or radial build, the strip is entirely severed and the free end attached to the core in any suitable manner such as by tack welding.

Fig. 3.illustrates-how the embryonic joint 3 in the core I maybe completed or severed by means of a pair of oppositely tapered wedges I5 and [6 which are driven between the arbor plate 8 transverse bars I! to which the shaft '1 is attached. By driving these wedges in from opposite directions the joint 3 is put under tension until finally, as shown in Fig. 4, the joint 3 breaks open. As the maximum tension is applied to the innermost layer the individual weakened places will rupture successively from the inside layer to the outside layer.

The operation shown in Figs. 3 and 4 maybe performed either before or after the core is annealed.

After the core has been cornpletedit is flexed into the position shown in Fig. 5 so. that a pre formed conductive winding may be slipped on to the winding leg 2, after which the joint 3 is closed by fitting its staggered ends together.

In some cases it may be desirable to further weaken the strip by forminga groove in the uncut center portion which groove is indicated at H! in Fig. 7. This can readily be accomplished by making the center part of thenotch 12 into a sharp chisel-like edge which, when forcedagainst the strip 5, forms the groove Hi. It will, however, beapparent that the invention is not limited to any particular way of weakening the strip and that it could be readily weakened by providing a. groove similar to [8 entirely across the strip without. actuallycutting through any portion of the strip.

Another way of breaking the joint is by shearing it sidewise. This is illustrated in Figs. 8 and 9 in which the winding leg 2 of the core is supported by a block 19 with thejoint extending beyond the edgeof the block. A pressure memberZD, such as the working part of a hydraulic press, may then, be brought to bear against the overhanging portion of the core so as to shear the .joint, 3 apart sidewise.

Still another way of breaking open the joint is by merely bending the core back and forth slightly at the, joint a fewtimes. It has been found that such back and forth bending will quickly cause the individualweakened places to break.

All of the above. ways of breaking the core joint open producevery smooth breaks which are entirely free irom sidewise extending burrs onthe laminations so that there is a minimum of diiiiculty from short circuits between the laminations at the joint, and the staggered ends or the joint caneasily be fitted together after the joint has been separated.

The invention is, of course, not limited to the formation of a conventional two-step lapped joint, and by properly orienting the successive weakened places in the core, which is merely a matter of predetermining the space bStWQBl'l-SHC: cessive weakened places in the strip priorto winding it on to the core, all of the weakened places can be made to lie in a single plane so as to form a butt joint or they can be made to lie in three or more planes so as to form a three or more stepped joint.

While there have been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that changes and modifications can be made without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention,

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of making a jointed wound magnetic core for electric apparatus comprising, weakening the tensile strength of a strip of magnetic material at a plurality of predetermined diiierently spaced places therein, winding said strip fiat-wise into a closed multi-Layer magnetic core having at least one of said weakened places in each layer lying within a transverse zone through said core which is relatively short in comparison with the circumference of said core, and mechanically severing said core at said weakened places in said zone so as to form a joint in said core at said zone.

2. The method of making a jointed wound magnetic core for electric apparatus comprising, weakening the tensile strength of the strip of magnetic material at a plurality of predetermined difierentlyspaced places therein, winding said strip fiat-wise into a multi-layer closed magnetic core having a straight winding leg with at least one of said weakened places in each layer lying within a transverse zone through said core which is relatively short in comparison with the circumference of said core, said zone being within the lateral confines of said winding leg and near one end thereof, said weakened places in said zone being successively offset from each other in a regular pattern, and mechanically breaking said weakened places in said zone so as to form a joint for said core in said zone.

3. The method of making a joint in a closed wound magnetic core for electric induction apparatus including, winding a strip of magnetic material on a mandrel to form a multi-layer closed core, simultaneously with said winding operation repeatedly partially cutting through 6 said strip so as to form a weakened place in each layer with said weakened places in a relatively narrow transverse Zone in said core, and applying a rupturing force to said core at said zone so as to break said weakened places and form a core joint.

4. The method of making a joint in a closed wound magnetic core for electric induction apparatus including, winding a strip of cold rolled high reduction silicon steel on a mandrel to form a multi-layer closed core, simultaneously with said winding operation repeatedly partially severing said strip so as to form a weakened place in each layer with said weakened places in a relatively narrow transverse zone in said core, and applying a rupturing force to said core at said zone parallel to the planes of said layers so as to break said weakened places and form a core joint.

5. The method of making a magnetic core comprising, attaching a strip of magnetic material having a most favorable magnetic direction lengthwise thereof to a rotatable mandrel, simultaneously rotating said mandrel so as to wind said strip thereon into a multi-layer closed core and repeatedly partially cutting through said strip at such lengthwise separated places that the weakened portions of said strip produced by said partial cuts occur at least once in each layer and lie in a relatively narrow transverse zone through said wound core, and applying oppositely directed tension forces to said core parallel to the planes of its layers on opposite sides of said zone so as successively to break said weakened portions in said layers and thereby form an openable and closable joint in said core for facilitating linking it with a conductive winding.

CHARLES W. MOODY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,594,526 Hume Aug. 3, 1926 1,935,426 Acly Nov. 14, 1933 1,942,264 Sternad Jan. 2, 1934 2,222,842 Humphrey Nov. 26, 1940 2,423,810 Goulding July 8, 1947 2,444,463 Nordquist July 6, 1948 2,478,030 Vinneau Aug. 2, 1949 2,543,089 Zimsky Feb. 27, 1951 2,548,628 Somerville Apr. 10, 1951 

